US2852667A - Overload control circuits for switch and lock movements - Google Patents

Description

OVERLQAD (CONTRGL (IIRCKHTS FOR SWITCH AND 06K MDVEMENTS Harvey A. Haines, Philadelphia, Pa, assiguor to Westinghouse Air Brake (lamp-any, Wilmerding, Pa, a corporation of Pennsylvania Application May 26, 1953, Serial No. 357,487

4 Claims. (Cl. 246242) My invention relates to control circuits for switch and lock movements, and in particular to circuits for controlling an electric switch and lock movement to cause several automatic operations of the movement in the event it fails to lock up the switch in its full normal or full reverse position on its first operation due, for example, to the presence of some obstruction.

Electric switch and lock movements are used in many locations along a railroad, and in particular are used at remote interlocking and where movable frogs are employed. When these switch and lock movements are remotely controlled they are usually not directly under the scrutiny of any person. In case some obstructing matter gets between a rail and an open switch point or a rail and a movable point frog, if the switch and lock movement is energized to reverse the switch and lock movement, it will be unable to complete its movement due to the presence of the obstructing matter. In the past in order to protect the motor under such circumstances, an overload relay has been provided which relay operates a brief interval after the motor becomes overloaded and deenergizes the motor. Thereafter, the operator in order to regain control of the movement is required to either return the switch control lever to its original position, thereby restoring the switch to its original position, or to operate the lever between its two positions in a manner to rock the switch points, in the hope of pulverizing the obstruction, thereby permitting the switch to complete its movement to the desired extreme position. This is time consuming and is therefore undesirable.

An object of my invention is to provide apparatus for automatically controlling an electric switch and lock movement in a manner to try to automatically crush or dislodge any obstruction which tends to prevent the switch points from completing their movement to an extreme position.

A further object of my invention is to provide control circuits for an electric switch and lock movement which, upon the switch motor becoming overloaded, will automatically become efitective to reverse the direction of operation of the switch and lock movement and return it to its normal position whereupon the switch will again automatically reverse and move toward the desired position. If, after making a sufficient number of attempts to lock the switch in the desired position the switch and lock movement is still unable to do so, the switch motor will become deenergized.

According to my invention, I provide an overload relay in series with the armature of the switch and lock movement motor. I further provide a control lever and a control relay. If it is desired to operate the switch and lock movement from one extreme position to the other, for instance from its normal to its reverse position, the control lever is thrown to its reverse position and the motor will become energized in such a direction as to operate the switch and lock movement to its reverse position. The control circuit means for the motor ice includes back contacts of the control relay, reverse contacts of the control lever, a contact of a circuit controller closed except when the switch and lock movement is in its reverse position, and a contact closed only when the overload relay is released.

Therefore, if the apparatus is operating properly, the switch and lock movement will move to its reverse position where the motor will become deenergized due to the circuit controller contact opening. However, if there is some obstruction which prevents the switch and lock movement from operating to its reverse position, the motor will become overloaded and the overload relay will operate, thereby deenergizing the motor. Upon the overload relay operating, a circuit will be established for energizing the control relay. When the control relay becomes energized, the polarity of the energization of the motor will become reversed, and with the overload relay now released due to the reversal of the polarity of the control circuit means, the motor will be reenergized in such a manner as to return the switch and lock movement to its normal position. The control relay is provided with a stick circuit which will remain closed until the switch and lock movement is returned to its normal position at which time the control relay will release and reestablish the energizing circuit for operating the switch and lock movement to its reverse position.

Accordingly, if the obstruction is not removed, the switch and lock movement will continuously operate between the normal and the obstructed position. In order to stop this action after a period of time, a time element means is provided which becomes energized upon the original energization of the control relay and which is further provided with circuit means for continuously supplying energy to the time element means. After a predetermined time interval, the time element means will operate to close its front contact and upon that occuring, the motor will be deenergized and will remain deenergized until the apparatus is reset.

Other objects of my invention will be described hereinafter as the characteristic features of construction and mode of operation of my novel control circuits are described in detail.

The single accompanying drawing is a diagrammatic view of control apparatus embodying my invention for a switch and lock movement used in conjunction with a railway switch.

It is to be understood that although I shall herein describe my novel control appaartus for switch and lock movements in conjunction with a railway switch, my invention is useful at many other places where electric switch andlock movements are used such as, for instance, at movable frogs and power operated derails.

Referring now to the drawing, the reference characters 1 and 2 designate the track rails of a stretch of railway track over which traffic normally moves in the direction indicated by the arrow. This stretch is provided with insulated joints 3 which insulate a track section H from the remainder of the stretch. A siding made up of the track rails 4 and 5 is connected to the main stretch of track by a railway switch 5. Section IT is provided with a track circuit including a track battery 1TB and a track relay lTR. A portion of the siding is included in this track circuit, rail 5 being connected to rail 1 by the frog arrangement and rail 4 being connected to rail 2 by ajumper 6.

At a control location either remote from or adjacent to the switch S is a control lever K which may occupy either a left-hand or a right-hand position. The control lever K has contacts which are herein illustrated as circles having the letter L or R associated therewith depending on whether the contact is closed in the levers left-hand or L position or in its right-hand or R position.

A polarized relay WR having both neutral and polar contacts is provided in this circuit arrangement. The polar contacts are of the well-known magnetic stick type and for purposes of explanation are assumed to be operated to the left-hand position, as shown, or to the opposite position in response to energization of the relay winding depending upon whether the current flows from left to right or in the opposite direction through the winding, and, upon deenergization of the relay winding to remain in the position to which they were last moved. The neutral contact will be closed when current flows through the winding of relay WR in either direction and will be open when the relay is deenergized. Relay WR partially controls the energization of a motor M having an armature A and a field winding F. Motor M is the power means for moving the switch points of switch S between their normal and reverse positions. Mechanically connected with motor M are circuit controller contacts 7, 8, 9 and 1b. Contact 7 is closed except when switch S is in its normal position and contact 8 is closed except when switch S is in its reverse position. Contacts 9 and 10 are of the type which are closed only when the switch is in its full normal or full reverse position, respectively.

An overload relay OR having a pickup winding 11 and a stick winding 12 is also provided. Pickup winding 11 is connected in series with armature A of motor M, and connected in multiple with winding 11 is a resistor X. Preferably, resistor X has a positive temperature coeificient of'resistance, that is, the resistance of the resistor increases as its temperature increases. The various parts are so arranged and proportioned that during normal operation of motor M, most of the current taken by the motor flows through resistor X, and little current flows through winding 11 so that the relay remains released. However, when motor M becomes overloaded and armature A commences to draw a heavy current for an extended period of time, the resistor X will become heated to such a degree that its resistance will sharply increase, thereby causing a larger proportion of the armature current to flow through winding 11, which will result in relay OR picking up. Winding 12 of relay OR is included in a stick circuit for relay OR, which circuit will be traced subsequently. Relay OR has a special contact structure which is usually referred to as a continuity transfer contact and is shown schematically in the drawing. This contact structure comprises contact fingers 13, 14- and 15. Contact finger 13 is biased by its own resiliency to a position in which it engages a fixed contact finger 14 to close a contact 1314-. When relay OR becomes energized to the point where its armature picks up, the first part of the movement of the armature causes contact finger 15 to move into engagement with the downwardly projecting end of finger 13 and closes a contact 13-15 with contact 13-14 remaining closed, but the subsequent movement of the armature causes finger 13 to move out of engagement with finger 14 and thus open contact 13-14. Contact 1315, however, then remains closed. Overload relay OR is also provided with a contact 16 which cooperates with winding 12 to prevent relay OR from picking up on transient overloads such as when motor M is starting. It will be seen that with relay OR released and contact 16 closed, winding 12 is short-circuited, thereby providing relay OR with a slow pickup characteristic. Unless an overload is more than transient, relay OR will not pick up. If the overload is for an appreciable length of time, relay OR will pick up and open the obvious snubbing circuit.

A repeater relay ORPR is controlled by overload relay OR, and in turn partially controls a control or stick relay PSR. Relay PSR controls repeater relay PPSR, and a push button PB, located at the control location, is used at times to deenergize relay PPSR. Relay PPSR controls the energization of a time element relay TER,

' here shown as a thermal relay of well known construction. Upon energization of the thermal relay, its heating element H will commence generating heat and thereby cause a bimetallic element (not shown) to start moving from a first or deenergized position to a second or energized position. Upon relay TER becoming energized, its back or checking 'contact b will become open almost immediately and and when relay TER has been energized for a predetermined time interval, its front contact a will become closed.

Relay controls a repeater relay TEPSR. A relay NWCR is controlled by circuit controller contact 9, which is closed only when switch S is in its normal position, and a relay RWCR is controlled by circuit controler contact 10, which is closed only when switch S is in its reverse position. The energy for operating motor M and the several relays heretofore described, except track relay 1TR, is supplied by a suitable source of energy such as a battery LB having a positive terminal B and a negative terminal N.

As shown in the drawing, the arrangement is in the condition it assumes when the switch S is in its normal position, that is the position in which traflic will move directly along the single stretch of track and not into the siding. Lever K is in its normal or left-hand position thereby causing its L contacts to be closed and its R contacts to be opened. Track relay 1TR is energized by its track battery 1TB and its front contacts are therefore closed. Relay WR is energized so that its neutral contact a is closed and its polar contacts b and c are in their normal or left-hand position. The energizing circuit for relay WR may be traced from positive terminal B of battery LB, over back contact b of relay TEPSR, back contact d of relay PSR, contact L2 of lever K, front contact b of relay 1TR, contact 1314 of relay OR, the winding of relay WR from left to right, front contact a of relay 1T R, contact L1 of lever K, and back contact c of relay PSR to negative terminal N of battery LB. With the switch in its normal position circuit controller contact 7 will be open, circuit controller contact 8 will be closed, circuit controller contact 9 will be closed and circuit controller contact 10 will be open. With circuit controller contact 9 closed, relay NWCR will be energized by a circuit which may be traced from positive terminal B of battery LB, over contact 9, and the winding of relay NWCR to negative terminal N of battery LB. All other relays heretofore mentioned will, at this time, be deenergized.

Assuming it is now desired to move the switch to its reverse position, control lever K will be moved from its L to its R position, thereby opening its L contacts and closing its R contacts. Accordingly, relay WR will become energized by a second energizing circuit which may be traced from positive terminal B of battery LB, over back contact b of relay TEPSR, back contact 0! of relay PSR, contact R1 of lever K, front contact a of relay 1TR, the winding of relay WR from right to left, contact 1314 of relay OR, front contact b of relay 1TR, contact R2 of lever K, and back contact 0 of relay PSR to negative terminal N of battery LB. Accordingly, neutral contact a of relay WR will open and reclose as the polarity is reversed and the polar contacts of relay WR will move to their reverse or right-hand position. This movement of the polar contacts of relay WR to their reverse position will establish a circuit for energizing motor M so that it will move the switch points to their reverse position, which circuit may be traced from positive terminal B of battery LB, over neutral contact a of relay WR, reverse contact b of relay WR, winding 11 of relay OR in multiple with resistor X, armature A of motor M, reverse contact 0 of relay WR, circuit controller contact 8, and the field winding F of motor M to negative terminal N of battery LB. Therefore, motor M will start rotating in the direction to move the switch points to their reverse 'position and will conassae er i tinue to operatein that direction until switch 5 occupies its extreme reverse position wherein circuit controller contact 8 becomes open and the motor will become deenergized. While the motor is operating, switch circuit controller contacts 9 and lit will both be open and, accordingly, relay NWCR will release and relay RWCR will remain released. When the switch is in its extreme reverse position, contact 10 will be closed. and relay RWCR will be energized.

It will be obvious that with the switch S locked in its reverse position, if lever K is moved to its left-hand or L position, relay WR will be energized so that it will operate its polar contacts to their normal or left-hand position and motor M will become energized so as to move the switch S to its normal position at which time the motor will again become deenergized.

Assuming that the switch S is returned to its normal position, let it further be assumed that some obstruction finds its way in between the open switch point and rail 2. If it is now desired to reverse the switch, lever K will be thrown to its R position thereby reversing the flow of current through relay WR, which will operate its polar contacts to their reverse or right-hand position, as was previously described. Accordingly, motor M will commence moving the switch points to their reverse position and upon the switch S moving out of its normal position, contact 9 will open and relay NWCR will become deenergized.

When the switch point comes into contact with the obstruction, the motor M will commence drawing an abnormally heavy current. As the motor current increases, the resistance of resistor X will increase due to its positive temperature coefficient, and a larger proportion of the motor current will flow through Winding 11 of relay OR. Accordingly, after a time delay afforded by the snubbing circuit including contact to, relay OR will operate its armature and contact finger 15 will come into contact with contact finger 13, thereby opening contact l314 and closing contact ll315, as was previously described. Accordingly, relay ORPR will become energized by a circuit which may be traced from positive terminal B of battery LB, over back contact I) of relay TEPSR, back contact d of relay PSR, contact R1 of lever K, front contact a of relay lTR, the winding of relay ORPR, winding 12 of relay OR, contact l3--15 of relay OR, front contact [2 of relay llTR, contact R2 of lever K, and back contact 0 of relay PSR to negative terminal N of battery LB. Furthermore, since contact 16 of relay OR is now open it will be seen that the holding or stick winding 12 of relay OR will now also be energized over this energizing circuit for relay ORPR. With relay ORPR picked up, a pick up circuit will be established for relay PSR, which circuit may be traced from positive terminal B of battery LB, over front contact a of relay ORPR, checking contact b of relay TER, and the winding of relay PSR to negative terminal N of battery LB. Upon relay PSR becoming energized and picking up, a stick circuit will be closed for continuously energizing relay PSR as long as relay NWCR remains deenergized, which stick circuit may be traced from positive terminal B of battery LB, over contact R3 of lever K, back contact a of relay NWCR, front contact a of relay PSR, and the winding of relay PSR to negative terminal N of battery LB.

Upon relay PSR picking up and sticking up, a circuit will be closed for energizing relay PPSR, which circuit may be traced from positive terminal B of battery LB, over front contact 12 of relay PSR, the winding of relay PPSR, and push button PB to negative terminal N of battery LB. Upon relay PPSR being energized, a stick circuit for maintaining relay PPSR energized will be established, which circuit may be traced from positive terminal B of battery LB, over front contact 0 of relay lTR, front contact a of relay PPSR, the winding of relay PPSR, and push button PB to negative terminal N of battery LB. With relay PPSR now picked up, a circuit will be established for energizing the heating element H of relay TER, which circuit may be traced from positive terminal B of battery LB, over front contact [2 of relay PPSR, the heating element H of relay TER, and back contact a of relay TEPSR to negative terminal N of battery LB. Accordingly, the heating element of relay TER will be fully energized until its repeater relay TEPSR picks up and as long as relay PPSR remains stuck up. Therefore, checking contact b of relay TER will open and thereby open the previously traced energizing circuit for relay PSR. However, relay PSR will now be held energized by its stick circuit which does not include checking contact 12 of relay TER.

Furthermore, upon relay OR picking up, the previously traced energizing circuit for relay WR will become open at contact ]l3-l4 of relay OR and, accordingly, relay WR will become deenergized and its neutral contact a will open. Therefore, motor M will become deenergized and no current will flow through winding 11 of relay OR. Upon relay PSR picking up, it will pole change the previously traced energizing circuit for relay ORPR and winding 12 of relay OR and, as the flux produced in winding 12 decreases while it reverses direction, the armature of relay OR will release, thereby closing contact 1314 and opening contact 13-15. Upon the release of relay OR, an energizing circuit will be established for energizing relay WR in the direction to cause it to operate its polar contacts to their normal or left-hand position whereupon the neutral contact a of relay WR will close. This circuit may be traced from positive terminal B of battery LB, over back contact b of relay TEPSR, front contact 0 of relay PSR, contact R2 of lever K, front contact 17 of relay lTR, contact 13-14 or relay OR, the winding of relay \VR from left to right, front contact a of relay lTR, contact R1 of lever K, and front contact d of relay PSR to negative terminal N of battery LB. Accordingly, motor M will commence operating in the direction to return the switch points to their normal position.

Furthermore, upon the release of relay OR, current will cease flowing through the winding of relay ORPR and accordingly, relay ORPR will release. Therefore, the energizing circuit for relay PSR will become open at a second point, front contact a of relay ORPR. When the switch points return to their normal position, relay NWCR will become energized because circuit controller contact 9 will become closed, and, accordingly, relay NWCR will pick up and open its back contact a. Therefore the stick circuit for relay PSR will become open and relay PSR will release.

Upon relay PSR releasing, the previously traced energizing circuit for relay PPSR will become open at front contact I) of relay PSR, but relay PPSR will remain energized over its previously traced stick circuit. Therefore, relay TER will continue to be energized. Furthermore, upon the release of relay PSR, pole changing contacts c and d of relay PSR will release and, accordingly, the energizing circuit which has already been traced for energizing relay WR in its reverse direction will once more become established. Therefore, motor M will become energized in the direction to move the switch points toward their reverse position in a manner which has already been described. If the obstruction still remains, relay OR will again operate, thereby causing relay ORPR to again'pick up. Upon relay ORPR picking up, a second energizing circuit for relay PSR will become established which circuit may be traced from positive terminal B of battery LB, over front contact a of relay ORPR, front contact 0 of relay PPSR, and the winding of relay PSR to negative terminal N of battery LB. Accordingly, relay PSR will pick up, thereby reversing the polarity of the energizing circuit for relay WR. Therefore, relay WR will reverse its polar contacts, thus reversing the polarity of motor M and causing the switch to return to its normal position where relay PSR will again release to commence the repeating of the cycle. The second energizing circuit for relay PSR is necessitated by the fact that upon the energization of relay TER, checking contact b of relay TER will become open and will stay open until after relay TER closes its front contact a. Accordingly, each time relay PSR picks up after its initial picking up, the energy is supplied over the second energizing circuit.

As was previously stated with relay OR picked up, relay PPSR will become energized and will remain stuck up over its previously traced stick circuit. Therefore, even after relay OR releases, relay PPSR will remain picked up and will continue to energize the heating element H of relay TER. While the switch points are being moved back and forth between their normal position and the position in which the obstruction causes the motor to become overloaded, the contacts of relay TER are being moved to their operated or energized position and, after the expiration of the predetermined time interval, front contact a of relay T ER will close. Accordingly, an energizing circuit will be established for relay TEPSR, which circuit may be traced from positive terminal B of battery LB, over front contact b of relay PPSR, front contact a of relay TER, and the winding of relay TEPSR to negative terminal N of battery LB. Upon the picking up of relay TEPSR, a stick circuit will be established for that relay which circuit may be traced from positive terminal B of battery LB, over front contact b of relay PPSR, the heating element H of relay TER, front contact a of relay TEPSR, and the winding of relay TEPSR to negative terminal N of battery LB. This insertion of the winding of relay TEPSR in series with the heating element H of relay TER will reduce the energization of heating element H sufficiently to allow front contact a of relay T ER to open, but relay TEPSR will remain picked up over the previously traced stick circuit.

Upon the picking up of relay TEPSR, the energizing circuits for relay WR, which circuits have already been traced, will become open at back contact b of relay TEPSR and, accordingly, relay WR will become deenergized and neutral contact a of relay WR will become open. With neutral contact a of relay WR opened, all energizing circuits for the motor M will become open and, accordingly, the motor will stop operating. Furthermore, until the return push button PB is operated to open the stick circuit for relay PPSR, thereby causing relay PPSR to release, it will be impossible to operate the switch S in either direction. However, when the push button PE is operated, the stick circuit for relay PPSR will become open and relay PPSR will release, thereby deenergizing relays TER and TEPSR. Relay TER will release its contact b and relay TEPSR will release its contacts. Switch S may now be restored to its normal position by moving lever K back to its normal or L position which will energize motor M in a direction to operate the switch points to their normal position.

It should be pointed out that my apparatus is provided with an interlocking feature which will prevent switch S from being reversed while a train is occupying section IT. This is accomplished by including in the energizing cir cuits for relay WR, front contacts a and b of relay ITR. With such an arrangement, when a train occupies section 1T, relay lTR will be released, thereby deenergizing relay WR. Accordingly, the two energizing circuits for motor M will be open at neutral contact a of relay WR and motor M cannot be energized to operate switch S.

My invention is particularly useful where the obstruction is made of some brittle material such as coal or ice because with the switch points coming repeatedly into contact with the obstruction, it is highly probable that the obstruction will be pulverized and thereby eliminated so that the switch will eventually become locked in the desired position without any assistance from the operator. This was not possible with the previously available arrangements because the motor upon becoming overloaded merely became deenergized and thereafter the operator had to rock the switch by moving lever K between its two positions.

Although I have herein shown and described only one form of overload protection circuit arrangement embodying my invention, it is to be understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention. 7

Having thus described my invention, what I claim is:

1. In combination with an electric vswitch and lock movement which is operable between a first and a second position and which includes an electric motor as a driving means, position selecting means which may occupy a first or second position, an overload relay which is in a first condition when said .motor is not overloaded and is in a second condition when said motor is overloaded, a control relay, a stick repeater relay for said control relay, a time element relay which operates after it has been energized for a predetermined time interval, circuit means for energizing said motor for operating said switch and lock movement from said first to said second position closed when said time element relay has not operated, said control relay is deenergized, said position selecting means is in said second position, and said overload relay is in said first condition; circuit means for energizing said motor for returning said switch and lock movement to said first position if said motor becomes overloaded while operating said switch and lock movement to said second position closed when said time element relay has not operated, said control relay is energized, said position selecting means is in said second position, and said overload relay is in said first condition; energizing circuit means for said control relay closed when said overload relay is in said second condition and when either said time element relay has not been energized or when said stick repeater relay has been picked up, stick circuit means for said control relay closed when said switch and lock movement is between said two positions, energizing circuit means for said time element relay controlled by said control relay, and stick circuit means for said time element relay.

2. In combination, a switch and lock movement operable between a first and a second position, an electric motor for operating said switch and lock movement between said two positions, a polarized relay provided with contacts which may occupy a first and a second position, an overload relay which picks up when and only when saidmotor is overloaded, a time element relay which operates only after it has been energized for a predetermined time interval, a control relay, a control lever which can occupy a first or a second position, a first circuit for energizing said polarized relay so that its contacts will operate to their second position including a back contact of said control relay and closed when said time element relay has not operated, said lever is in its second position, and said overload relay is released; a second circuit for energizing said polarized relay to said second position including a front contact of said control relay and closed when said time element relay has not operated, said lever is in its first position, and said overload relay is released; a first circuit for energizing the contacts of said polarized relay to their first position including a back contact of said control relay and closed when said time element relay has not operated, said lever is in its first position, and said overload relay is released; a second circuit for energizing said polarized relay to its first position including a front contact of said control relay and closed when said time element relay has not operated, said lever is in its second position, and said overload relay is released; a first contact associated with said switch and lock movement closed except when said switch and lock movement is in said second position, a second contact associated with said switch and lock movement closed except when said switch and lock movement is in said first position, a circuit for energizing said motor so that it will operate said switch and lock movement toward its first position including said second contact and closed when said polarized relay is energized to its first position, a circuit for energizing said motor so that it will operate toward its second position including said first contact and closed when said polarized relay is energized to its second position, a first energizing circuit for said control relay closed when said overload relay picks up and said time element relay is deenergized, a repeater rela a second energizing circuit for said control relay closed when said overload relay picks up and said repeater relay is picked up, a stick circuit for said control relay closed when said switch and lock movement is between its first and second positions, an energizing circuit for said repeater relay including a front contact of said control relay, a stick circuit for said repeater relay, and an energizing circuit for said time element relay including a front contact of said repeater relay.

3. In combination, a switch and lock movement connected to a track switch and having an electric motor to move the switch to its normal and reverse positions according as said motor is energized normal or reverse, an operating circuit means with connections to said motor and including a polarized relay for reversibly energizing the motor, a controller operated by said switch and lock movement and having contacts interposed in said operating circuit means to deencrgize said motor at the normal and reverse positions of the switch, said controller having other contacts closed at selected positions of the switch, an overload relay means having a winding interposed in said operating circuit means and a contact closed only when said motor draws an overload current, a control circuit having connections to said polarized relay and including in series a first and a second pole changer, said first pole changer to control said polarized relay to initiate a movement of the switch to either its normal or reverse position, circuit means controlled jointly by said overload relay contact and said other controller contacts to automatically operate said second pole changer to control said polarized relay to automatically and repeatedly move the switch toward one and then the other of its two positions when the motor becomes overloaded regardless of the initial movement of the switch, and a time element relay having a contact closed only when that relay is energized a predetermined time interval, circuit means including said overload relay contact to energize said time element relay and efiective when said overload relay is once energized due to an overload of said motor, and said time element relay contact interposed in said control circuit means to deenergize said polarized relay and stop said motor at the end of said time interval.

4. In combination, a switch and lock movement having an electric motor to move the movement between a normal and a reverse position according as said motor is supplied with current by a first or a second operating circuit, a polarized relay to selectively control said first and second operating circuits according as the relay is energized at normal or reverse polarity and to open the operating circuits when the relay is deenergized, a circuit controller operatedby said switch and lock movement and having contacts to open said first and second operating circuits at said normal and reverse positions of the movement respectively, an overload relay means having a winding connected to said operating circuits and a contact operated only when said motor draws an overload current, a control circuit connected to said polarized relay and having a first and a second pole changer, said first pole changer manually controlled to initiate movement of said switch and lock movement from either of its positions toward its other position, other controller contacts selectively operated by said switch and lock movement according to the position of the movement, a control relay to control said second pole changer, circuit means controlled jointly by said overload relay contact and said other contacts with connection to said control relay to energize and deenergize that control relay for automatically operating said switch and lock movement towards its two positions repeatedly when the motor becomes overloaded, a time element relay having a contact closed only when that relay is energized a predetermined time interval, circuit means controlled by said overload relay to energize said time element relay once said motor is overloaded, means controlled by said time element relay contact to open said control circuit at the end of said predetermined time interval and thereby deenergize said motor, and means to reclose the motor operating circuits.

References Cited in the file of this patent UNITED STATES PATENTS 1,630,667 Meyers May 31, 1927 1,781,880 OHagan Nov. 18, 1930 2,232,545 Lum Feb. 18, 1941 2,514,694 Chapman July 11, 1950 2,558,032 Andrews June 26, 1951 2,608,647 Johnston Aug. 26, 1952

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